The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657−415

Author： Mason A. B. Clark J. S. Norton A. J. Crowther P. A. Tauris T. M. Langer N. Negueruela I. Roche P.

ISSN： 0035-8711

Source： Monthly Notices of the Royal Astronomical Society, Vol.422, Iss.1, 2012-05, pp. : 199-206

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Abstract

ABSTRACTWe report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657−415 obtained in the H band using ISAAC on the Very Large Telescope.Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s⁻¹. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M_⊙ and a mass of 14.3 ± 0.8 M_⊙ for the Ofpe/WN9 highly evolved donor star.OAO 1657−415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657−415 becomes the ninth with a dynamically determined NS mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657−415 is much more highly evolved than the majority of the supergiant donors in other HMXBs, joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres.Considering the evolutionary development of OAO 1657−415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor’s envelope via spiral-in, ruling out a common envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO 1657−415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657−415 current orbital configuration.